Method for the safe induction of immunity against rsv

ABSTRACT

Methods of inducing a safe immune response against respiratory syncytial virus (RSV) in a human subject in need thereof, including administering to the subject a composition including recombinant adenovirus including a nucleic acid encoding an RSV Fusion (F) protein including the amino acid sequence of SEQ ID NO: 1, and a pharmaceutically acceptable carrier, in a total dose of from about 1×101° to about 2×10″ viral particles (vp), are described.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No. 16/642,082, filed on Feb. 26, 2020, which is a Section 371 of International Application No. PCT/EP2018/074710, filed Sep. 13, 2018, which was published in the English language on Mar. 21, 2019, under International Publication No. WO 2019/053109 A1 which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/558,994, filed Sep. 15, 2017, the disclosures of which are incorporated herein by reference in their entirety.

REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY

This application contains a sequence listing, which is submitted electronically via EFS-Web as an ASCII formatted sequence listing with a file name “Sequence_Listing_004852_159US2”, creation date of Jan. 7, 2022, and having a size of about 7.6 kB. The sequence listing submitted via EFS-Web is part of the specification and is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to methods for safely inducing effective immunity against

RSV. In particular, the invention relates to adenovirus serotype 26 expression vectors expressing RSV F protein providing the safe induction of immunity against multiple strains of RSV in human subjects.

BACKGROUND OF THE INVENTION

Respiratory syncytial virus (RSV) is a highly contagious childhood pathogen of the respiratory tract which is believed to be responsible for 200,000 childhood deaths annually. In children younger than 2 years, RSV accounts for approximately 50% of the hospitalizations due to respiratory infections, with a peak of hospitalization occurring at 2-4 months of age. It has been reported that almost all children will have experienced infection with RSV by the age of two, and repeated infection during life is attributed to low natural immunity. In the elderly, the RSV disease burden is similar to those caused by non-pandemic influenza A infections.

RSV is a paramyxovirus, belonging to the subfamily of pneumovirinae. Its genome encodes for various proteins, including the membrane proteins known as RSV Glycoprotein (G) and RSV fusion (F) protein which are the major antigenic targets for neutralizing antibodies.

Unlike the RSV G protein, the F protein is conserved between RSV strains; which makes it an attractive vaccine candidate able to elicit broadly neutralizing antibodies. The F protein is a transmembrane protein and it is incorporated in the virion membrane from cellular membrane during virus budding. The RSV F protein facilitates infection by fusing the viral and host-cell membranes. In the process of fusion, the F protein refolds irreversibly from a labile pre-fusion conformation to a stable post-fusion conformation. The protein precursor, F0, requires cleavage during intracellular maturation by a furin-like protease. There are two furin sites, cleavage of which results in removal of a p27 peptide and formation of two domains: an N-terminal F2 domain and a C-terminal F1 domain (FIG. 1). The F2 and F1 domains are connected by two cystine bridges. Antibodies against the fusion protein can prevent virus uptake in the cell and thus have a neutralizing effect. Besides being a target for neutralizing antibodies, RSV F contains cytotoxic T cell epitopes (Pemberton et al, 1987, J. Gen. Virol. 68: 2177-2182).

Despite 50 years of research, there is still no licensed vaccine against RSV. One major obstacle to the vaccine development is the legacy of vaccine-enhanced disease in a clinical trial in the 1960s with a formalin-inactivated (FI) RSV vaccine. FI-RSV vaccinated children were not protected against natural infection and infected children experienced more severe illness than non-vaccinated children, including two deaths. This phenomenon is referred to as ‘enhanced disease’.

Since the trial with the FI-RSV vaccine, various approaches to generate an RSV vaccine have been pursued. Attempts include classical live attenuated cold passaged or temperature sensitive mutant strains of RSV, (chimeric) protein subunit vaccines, peptide vaccines and RSV proteins expressed from recombinant viral vectors, including adenoviral vectors. Although some of these vaccines showed promising pre-clinical data, no vaccine has been licensed for human use due to safety concerns or lack of efficacy.

The most potent RSV neutralizing antibodies bind to a particular site (site zero) on the RSV F protein which is only exposed when the RSV protein is in its pre-fusion conformation which makes this particular conformation very attractive as a vaccine antigen. However, the F protein in its pre-fusion conformation is very unstable and readily undergoes a major conformational shift to the post-fusion conformation. Due to its instability the pre-fusion conformation thus has a propensity to prematurely refold into the stable postfusion conformation. This phenomenon is an intrinsic feature of the protein both in solution and on the surface of the virions.

Vaccine candidates based on the RSV F protein have failed due to problems with e.g. stability, purity, reproducibility, and potency. Indeed, despite many efforts to produce a vaccine against RSV that contain pre-fusion forms of RSV F protein, no stable pre-fusion RSV F polypeptides have been described that have been tested in humans.

Therefore, a need still exists for safe and effective vaccines and methods of vaccinating against RSV. The present invention aims at providing such methods for vaccinating against RSV in a safe manner.

SUMMARY OF THE INVENTION

According to the present invention it has for the first time been demonstrated that recombinant adenovectors expressing RSV F protein stabilized in the pre-fusion comformation induce a safe and effective (immunogenic) immune response against RSV when administered to human subjects.

The invention thus provides a method of inducing a safe immune response against respiratory syncytial virus (RSV) in a human subject in need thereof, comprising administering to the subject a composition comprising recombinant adenovirus comprising nucleic acid encoding an RSV Fusion (F) protein comprising the amino acid sequence of SEQ ID NO: 1, and a pharmaceutically acceptable carrier, in a total dose of from about 1×10¹⁰ to about 2×10¹¹ viral particles (vp) of adenovirus.

In a further aspect, the invention provides a vaccine composition comprising recombinant adenovirus comprising nucleic acid encoding an RSV Fusion (F) protein comprising the amino acid sequence of SEQ ID NO: 1, and a pharmaceutically acceptable carrier, in a total dose of about 1×10¹⁰ to about 2×10¹¹ viral particles (vp), for use in a method of inducing a safe immune response against respiratory syncytial virus (RSV) in a subject in need thereof.

In certain embodiments of the invention, the total dose is from about 5×10¹⁰ to about 1×10¹¹ viral particles (vp) of adenovirus. In certain embodiments, the dose is about 5×10¹⁰ or about 1×10¹¹ vp of adenovirus.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: Schematic representation of the RSV F protein. A protein precursor includes F2 and F1 domains and p27 peptide that is removed from the mature proteins by cleavage with furin-like proteases. The cleavage sites are indicated by arrows. The numbers on top of the boxes indicate amino acid positions in the full length protein excluding signal peptide. In the F1, structural elements are shown: fusion peptide (FP), refolding region 1 (RR1) including heptad repeat A (HRA) and refolding region 2 (RR2) including heptad repeat B (HRB).

FIG. 2: Relative surface expression of F protein variants. Full length variants of F protein were expressed in HEK293T cells. The cell were stained with anti-RSV F antibody (CR9503) and analyzed by Flow Cytometry (FACS). The Mean Fluorescent Intensity (MFI) values were calculated and normalized to MFI of control F wild type (Fwt)-transfected cell sample. The MFI of Fwt was set to 1. Bars represent mean values, error bars represent range of values.

FIG. 3: Fraction of pre-fusion F protein on cell surface. Full length variants of F protein were expressed in HEK293T cells. The cell were stained with anti-RSV F antibody CR9503 and anti-pre-fusion RSV F antibody CR9501 and analyzed by Flow Cytometry. The Mean Fluorescent Intensity (MFI) values were calculated and MFI measured by CR9501 was normalized to MFI measured by CR9503. The normalized MFI values indicate fraction of the pre-F on the cell surface. Bars represent mean values, error bars represent range of values.

FIG. 4: Relative surface expression of F protein variants. Soluble versions with the transmembrane region and cytoplasmic region deleted (Fsl) and full length variants of F protein were expressed in HEK293T cells. The expression level of the soluble protein was measured in the culture supernatant by octet and the full length variants were tested by cell staining using anti-RSV F antibody (CR9503) and analyzed by Flow Cytometry. The Mean Fluorescent Intensity (MFI) values were calculated and normalized to MFI of control F wild type (Fwt)-transfected cell sample. The MFI of Fwt was set to 1. Bars represent mean values, error bars represent range of values.

FIG. 5: Temperature stability of the F protein variants. Full length variants of F protein were expressed in HEK293T cells. After heat-shock, the cell were stained with anti-RSV F antibody (CR9501—solid lines and CR9503—dashed lines) and analyzed by Flow Cytometry. The percentage of cells positive for the staining was determined. Symbols represent mean values, error bars represent range of values. (A) The percentage of cells positive for the staining was determined. (B) The Mean Fluorescent Intensity (MFI) values were calculated and normalized to MFI of 37 C cell sample. The MFI of 37° C. sample was set to 1. Dotted lines correspond to background staining at 60° C.

FIG. 6: Stability of the F proteins. PreF is more stable than FA2 protein in prefusion conformation on the cell surface in the heat-stress assay. A549 cells were infected with Ad26 and Ad35 comprising the insert FA2 (wt RSV F, grey bars) or prefusion F stabilized insert (preF2.2, black bars) at the indicated MOI. The cells were temperature treated at the indicated temperature for 15 minutes before staining. Top: percentage of cells presenting prefusion F on their surface (detected by CR9501 antibody); bottom: percentage of cells presenting any form of the F protein, prefusion and post fusion (detected by CR9503 antibody). The values were normalized to 37° C. samples. All bars represent a single measurement.

FIG. 7: Ad26.RSV.preF2.1 and F2.2 elicit a cellular immune response after single administration in mice. Horizontal bars depict the geometric mean of the response within a group. The background level is calculated as the 95% percentile of the spot forming units (SFU) observed in non-stimulated splenocytes, and is indicated with a dotted line.

FIG. 8: Ad26.RSV.preF2.1 and F2.2 induce increased virus neutralizing antibodies when compared to Ad26.RSV.FA2, after single immunization in mice. Balb/c mice (n=4 per group) were immunized with the indicated dose of 108 to 1010 viral particles (vp) Ad26.RSV.FA2 or Ad26.RSV.preF2.1 or Ad26.RSV.preF2.2, or with formulation buffer, and humoral immune responses were assayed in the serum isolated 8 weeks after immunization. (A) Virus neutralizing antibodies were determined against RSV A Long using a micro-neutralization assay with an ELISA based read out. Titers are given as the log2 value of the IC50. (B) Pre-fusion or post-fusion F antibody titers were determined by ELISA, and the ratio between pre- and post-fusion F antibodies for all samples that showed pre- and post-fusion F titers above lower limit of quantification (LLoQ) was calculated. (C) Subclass ELISA was performed using post-fusion RSV F A2 as coating reagent, and the IgG2a/IgG1 ratio (log10) is plotted. Ratio's observed for Th1 (serum derived from animals immunized with RSV F expression Adenoviral vectors) and Th2 (serum derived from FI-RSV immunized animals) references samples are indicated with dashed lines. The LLoQ is indicated with a dotted lines (panels A), and horizontal bars represent the mean responses per group.

FIG. 9: Ad26.RSV.preF2.2 elicits antibody responses that neutralize a wide range of RSV isolates. Sera from Balb/c mice that were immunized with 1010 viral particles (vp) Ad26.RSV.FA2 (n=3) or Ad26.RSV.preF (n=4) or formulation buffer (n=2) were used in virus neutralization assays (micro-neutralization assay with an ELISA based read out) with the RSV A (upper panels) and B strains (lower panels) indicated. Titers are given as the log2 value of the IC50, and horizontal bars represent the mean response per group. LLoQ is indicated with a dashed line.

FIG. 10: Single immunization with Ad26.RSV.preF2.2 or Ad35.RSV.preF2.2 at low doses protects cotton rats against challenge with the homologous RSV A2. Cotton rats (Sigmodon hispidus) (n=7 to 9 per group) were immunized with the indicated doses (in vp/animal) of Ad26.RSV.preF2.2, Ad26.RSV.FA2 (left panels), Ad35.RSV.preF2.2 or Ad35.RSV.FA2 (right panels) by single intramuscular administration. Control immunizations were performed with formulation buffer, FI-RSV, or intranasal application of a low dose of RSV A2. At seven weeks post-immunization animals were challenged intranasally with 105 pfu RSV A2. The lung (A-B) and nose viral titers (C-D) were determined by plaque assay 5 days after challenge. (E-F) Sera taken just before challenge were used to perform a virus neutralizing assay with the RSV A Long strain (micro-neutralization assay with an ELISA based read out). The dotted line represents the lower level of quantification (LLoQ). Horizontal bars represent the mean titer per group.

FIG. 11: Ad26.RSV.preF2.2 or Ad35.RSV.preF2.2 immunization of cotton rats does not result in increased alveolitis scores after RSV A2 challenge. Cotton rats (Sigmodon hispidus) (n=7 to 9 per group) were immunized with the indicated doses (in vp/animal) of Ad26.RSV.preF2.2, Ad26.RSV.FA2 (upper panel), Ad35.RSV.preF2.2, or Ad35.RSV.FA2 (lower panel) by single intramuscular administration. Control immunizations were performed with formulation buffer, FI-RSV, or intranasal application of a low dose of RSV A2. At seven weeks post-immunization animals were challenged intranasally with 105 pfu RSV A2. Alveolitis was scored by histopathological examination of one lung lobe 5 days after challenge on a non-linear scale from 0 to 4. The horizontal dotted line marks the maximal score of the control animals that were pre-exposed to RSV-A2 before challenge to mimic a natural exposure to RSV that does not lead to ERD.

DETAILED DESCRIPTION OF THE INVENTION

Although respiratory syncytial virus (RSV) infects people throughout life, most people fail to mount a long lasting protective immune response. In addition, in the elderly the waning immune response contributes to increased susceptibility to severe disease after RSV infection causing significant morbidity and mortality. There are indications in the literature that both neutralizing antibody and T-cell mediated protection play a role in preventing RSV infection. It is therefore believed that a successful RSV vaccine, in particular for the elderly, should increase both potent neutralizing antibody levels and induce a robust T-cell response.

RSV infection induces virus specific antibodies which are mainly directed against the fusion (F) protein. The most potent RSV neutralizing antibodies found in human sera bind to a particular site (site Φ or site zero) on the RSV F protein, which is only exposed when the RSV protein is in its pre-fusion conformation which makes this particular conformation very attractive as a vaccine antigen. However, the F protein in its pre-fusion conformation is very unstable and readily undergoes a major conformational shift to the post-fusion conformation.

In the research that has led to the present invention, a stabilized RSV F protein was prepared with a unique set of amino acid mutations compared to the wild type RSV F antigen from the RSV A2 strain (Genbank ACO83301.1). By demonstrating specific binding in vitro to pre-fusion specific antibodies it was shown that indeed a stabilized RSV F antigen in the pre-fusion conformation was obtained.

According to the present invention, it has now been shown that the stabilized RSV F protein maintains its pre-fusion conformation in vivo, is immunogenic and can be safely administered to human subjects in need thereof.

Thus, according to the present invention methods are provided for inducing a safe immune response against RSV in a human subject in need thereof, comprising administering to the subject a composition comprising recombinant adenovirus comprising nucleic acid encoding an RSV Fusion (F) protein comprising the amino acid sequence of SEQ ID NO: 1, and a pharmaceutically acceptable carrier, in a total dose of from about 1×10¹⁰ to about 2×10¹¹ viral particles (vp) of adenovirus.

In a further aspect, the invention provides a vaccine composition comprising recombinant adenovirus comprising nucleic acid encoding an RSV Fusion (F) protein comprising the amino acid sequence of SEQ ID NO: 1, and a pharmaceutically acceptable carrier, in a total dose of about 1×10¹⁰ to about 2×10¹¹ viral particles (vp), for use in a method of inducing a safe immune response against respiratory syncytial virus (RSV) in a subject in need thereof.

In certain embodiments of the invention, the composition comprises recombinant adenovirus comprising nucleic acid encoding an RSV Fusion (F) protein comprising the amino acid sequence of SEQ ID NO: 1, and a pharmaceutically acceptable carrier, in a total dose of from about 5×10¹⁰ to about 1×10¹¹viral particles (vp) of adenovirus.

In certain embodiments, the dose is about 5×10¹⁰ or about 1×10¹¹ vp of adenovirus.

According to the present invention it has been shown that adenovirus encoding RSV F protein in the pre-fusion conformation (in particular the RSV F protein of SEQ ID NO: 1) is highly immunogenic. Humoral immune responses are increased as compared to similar doses of adenovirus encoding the wild-type RSV F protein, which is not stabilized in the pre-fusion conformation and likely quickly transitions into the post-fusion conformation upon expression.

In certain embodiments, the immune response comprises the induction of antibodies directed against RSV F protein. Thus, according to certain embodiments, the immune response comprises the induction of antibodies that specifically bind to the RSV F protein, as measured in an ELISA.

In certain embodiments, the immune response comprises the induction of RSV neutralizing antibodies. In certain embodiments, the neutralizing antibodies are capable of neutralizing RSV A and B strains. In certain embodiments, the immune response comprises the induction of antibodies that are capable of neutralizing RSV A and B strains in a VNA assay.

As used herein the “ induction of antibodies” means that the level of antibodies as measured after administration of composition comprising recombinant adenovirus expressing the RSV F protein of SEQ ID NO: 1 is higher than the level of antibodies prior to administration of said composition.

In certain embodiments, the immune response comprises the induction of antibodies specific for the RSV F protein in the pre-fusion conformation and antibodies specific for the RSV F protein in the post-fusion conformation, wherein the geometric mean titer (GMT) increase of antibodies specific for RSV F protein in the pre-fusion conformation is higher than the GMT increase of antibodies specific for RSV F protein in the post-fusion conformation, in enzyme linked immunosorbent assays (ELISAs). The methods of the present invention thus result in a larger increase of antibodies that are specifically binding to RSV F protein in the pre-fusion conformation as compared to antibodies that are specifically binding to RSV F protein in the post-fusion conformation. Without wishing to be bound to a particular theory, it is believed that this results in a more effective immune response since pre-fusion specific antibodies are thought to be more effective in neutralizing RSV virus, and thereby more effective in prevention RSV infection (Gilman M S, Castellanos C A, Chen M, Ngwuta J O, Goodwin E, Moin S M, Mas V, Melero J A, Wright PF, Graham B S, McLellan J S, Walker L M. Sci Immunol. 2016 Dec. 16; 1(6). pii: eaaj1879. doi: 10.1126/sciimmunol.aaj1879. Epub 2016 Dec. 9. Rapid profiling of RSV antibody repertoires from the memory B cells of naturally infected adult donors)

In certain embodiments, the ratio between the GMT increase of post-fusion F specific antibodies as measured in ELISA and the mean geometric titer increase of neutralizing antibodies as measured in a VNA assay is reduced after administration of said composition as compared to said ratio before administration of said composition. The methods of the present invention thus results in a more favourable composition of the RSV specific humoral response that favours neutralizing antibodies over binding antibodies.

In certain embodiments, the immune response further comprises a cellular response as indicated by IFNgamma producing T cells as measured in an IFNy ELISPOT in response to stimulation with a pool of peptides covering the F protein of SEQ ID NO: 1 and/or by measurement of CD4 and CD8 T-cell subsets expressing IFNγ, IL-2 and TNFα by intracellular staining (ICS) after stimulation with a pool of peptides covering the RSV F protein of SEQ ID NO: 1. It has been suggested that RSV specific T cells can support the prevention of infection and limit disease; this could be especially beneficial for the older adults since it has been described that the cellular response may decrease with age (Openshaw P J M, Chiu C, Culley F J, Johansson C. Annu Rev Immunol. 2017 Apr. 26; 35:501-532. doi: 10.1146/annurev-immunol-051116-052206. Epub 2017 Feb. 6. Protective and Harmful Immunity to RSV Infection.)

By inducing a safe and immunogenic immune response, the methods of the present invention can be used to prevent serious lower respiratory tract disease leading to hospitalization and to decrease the frequency of complications such as pneumonia and bronchiolitis due to RSV infection and replication in a subject.

As used herein, the terms nucleic acid, nucleic acid molecule, nucleic acid or nucleotide sequence, and polynucleotide are used interchangeably and all refer to the linear biopolymers (chains) made from nucleotides, including DNA and RNA. It will be understood by a skilled person that numerous different nucleic acid molecules can encode the same polypeptide as a result of the degeneracy of the genetic code. It is also understood that skilled persons may, using routine techniques, make nucleotide substitutions that do not affect the polypeptide sequence encoded by the polynucleotides described there to reflect the codon usage of any particular host organism in which the polypeptides are to be expressed. Therefore, unless otherwise specified, a “nucleic acid molecule encoding an amino acid sequence” includes all nucleotide sequences that are degenerate versions of each other and that encode the same amino acid sequence. Nucleotide sequences that encode proteins and RNA may include introns. Sequences herein are provided from 5′ to 3′ direction, as custom in the art.

In certain embodiments, the nucleic acid molecule encoding the RSV pre-fusion F protein are codon optimized for expression in mammalian cells, such as human cells. Methods of codon-optimization are known and have been described previously (e.g. WO 96/09378). In a preferred embodiment, the nucleic acid molecule encoding the RSV pre-fusion F protein comprises the nucleic acid sequence of SEQ ID NO: 2. In certain embodiments, the nucleic acid encoding the RSV F protein consists of the the nucleic acid sequence of SEQ ID NO: 2.

According to the invention, the subject in need thereof is a human subject. Preferably, the subject is an elderly subject, i.e. a human of 60 years and older. According to the present invention it has been shown that administration of recombinant adenovirus comprising nucleic acid encoding the RSV F protein in the pre-fusion conformation is safe and immunogenic, i.e. results in a potent humoral and cellular response, also in older subjects which may have a weakened immune system.

In certain embodiments, the recombinant adenovirus (also referred to as adenoviral vector) is a human recombinant adenovirus. The preparation of recombinant adenoviral vectors is well known in the art. The term ‘recombinant’ for an adenovirus, as used herein implicates that it has been modified by the hand of man, e.g. it has altered terminal ends actively cloned therein and/or it comprises a heterologous gene, i.e. it is not a naturally occurring wild type adenovirus.

In certain embodiments, the recombinant adenovirus according to the invention is deficient in at least one essential gene function of the E1 region, e.g. the E1a region and/or the E1b region, of the adenoviral genome that is required for viral replication. In certain embodiments, the adenovirus according to the invention is deficient in at least part of the non-essential E3 region. In certain embodiments, the adenovirus is deficient in at least one essential gene function of the E1 region and at least part of the non-essential E3 region. The adenoviral vector can be “multiple deficient,” meaning that the adenoviral vector is deficient in one or more essential gene functions in each of two or more regions of the adenoviral genome. For example, the aforementioned E1-deficient or E1-, E3-deficient adenoviral vectors can be further deficient in at least one essential gene of the E4 region and/or at least one essential gene of the E2 region (e.g., the E2A region and/or E2B region).

In certain embodiments, the adenovirus is a human adenovirus of the serotype 26 or 35. The vaccines according to the invention based on these serotypes appear more potent than the ones described in the prior art that were based on Ad5, since those failed to provide complete protection against RSV challenge replication after a single intramuscular administration (Kim et al, 2010, Vaccine 28: 3801-3808; Kohlmann et al, 2009, J Virol 83: 12601-12610; Krause et al, 2011, Virology Journal 8:375). The serotype of the invention further generally has a low seroprevalence and/or low pre-existing neutralizing antibody titers in the human population. Recombinant adenoviral vectors of these serotypes with different transgenes are evaluated in clinical trials, and thus far shows to have an excellent safety profile. Preparation of rAd26 vectors is described, for example, in WO 2007/104792 and in Abbink et al., (2007) Virol 81(9): 4654-63. Exemplary genome sequences of Ad26 are found in GenBank Accession EF 153474 and in SEQ ID NO:1 of WO 2007/104792. Preparation of rAd35 vectors is described, for example, in U.S. Pat. No. 7,270,811, in WO 00/70071, and in Vogels et al., (2003) J Virol 77(15): 8263-71. Exemplary genome sequences of Ad35 are found in GenBank Accession AC_000019 and in FIG. 6 of WO 00/70071.

A recombinant adenovirus according to the invention may be replication-competent or replication-deficient. In certain embodiments, the adenovirus is replication deficient, e.g. because it contains a deletion in the E1 region of the genome. As known to the skilled person, in case of deletions of essential regions from the adenovirus genome, the functions encoded by these regions have to be provided in trans, preferably by the producer cell, i.e. when parts or whole of E1, E2 and/or E4 regions are deleted from the adenovirus, these have to be present in the producer cell, for instance integrated in the genome thereof, or in the form of so-called helper adenovirus or helper plasmids. The adenovirus may also have a deletion in the E3 region, which is dispensable for replication, and hence such a deletion does not have to be complemented.

For non-subgroup C E1-deficient adenoviruses such as Ad35 (subgroup B) or Ad26 (subgroup D), it is preferred to exchange the E4-orf6 coding sequence of these non-subgroup C adenoviruses with the E4-orf6 of an adenovirus of subgroup C such as Ad5. This allows propagation of such adenoviruses in well known complementing cell lines that express the E1 genes of Ad5, such as for example 293 cells or PER.C6 cells (see, e.g. Havenga et al, 2006, J. Gen. Virol. 87: 2135-2143; WO 03/104467, incorporated in its entirety by reference herein). In certain embodiments, an adenovirus that can be used is a human adenovirus of serotype 35, with a deletion in the E1 region into which the nucleic acid encoding RSV F protein antigen has been cloned, and with an E4 orf6 region of Ad5. In certain embodiments, the adenovirus in the vaccine composition of the invention is a human adenovirus of serotype 26, with a deletion in the E1 region into which the nucleic acid encoding RSV F protein antigen has been cloned, and with an E4 orf6 region of Ad5.

In alternative embodiments, there is no need to place a heterologous E4orf6 region (e.g. of Ad5) in the adenoviral vector, but instead the E1-deficient non-subgroup C vector is propagated in a cell line that expresses both E1 and a compatible E4orf6, e.g. the 293-ORF6 cell line that expresses both E1 and E4orf6 from Ad5 (see e.g. Brough et al, 1996, J Virol 70: 6497-501 describing the generation of the 293-ORF6 cells; Abrahamsen et al, 1997, J Virol 71: 8946-51 and Nan et al, 2003, Gene Therapy 10: 326-36 each describing generation of E1 deleted non-subgroup C adenoviral vectors using such a cell line).

Alternatively, a complementing cell that expresses E1 from the serotype that is to be propagated can be used (see e.g. WO 00/70071, WO 02/40665).

For subgroup B adenoviruses, such as Ad35, having a deletion in the E1 region, it is preferred to retain the 3′ end of the E1B 55K open reading frame in the adenovirus, for instance the 166 bp directly upstream of the pIX open reading frame or a fragment comprising this such as a 243 bp fragment directly upstream of the pIX start codon (marked at the 5′ end by a Bsu36I restriction site in the Ad35 genome), since this increases the stability of the adenovirus because the promoter of the pIX gene is partly residing in this area (see, e.g. Havenga et al, 2006, J. Gen. Virol. 87: 2135-2143; WO 2004/001032, incorporated by reference herein).

The nucleic acid encoding the RSV F protein of SEQ ID NO: 1 can be introduced into the adenovirus for instance by standard molecular biology techniques. It can for instance be cloned into a deleted E1 or E3 region of an adenoviral vector. The nucleic acid (or transgene) is generally operably linked to expression control sequences. This can for instance be done by placing the nucleic acid encoding the RSV F protein under the control of a promoter. Further regulatory sequences may be added. Many promoters can be used for expression of a transgene(s), and are known to the skilled person. A non-limiting example of a suitable promoter for obtaining expression in eukaryotic cells is a CMV-promoter (U.S. Pat. No. 5,385,839), e.g. the CMV immediate early promoter, for instance comprising nt. −735 to +95 from the CMV immediate early gene enhancer/promoter. A polyadenylation signal, for example the bovine growth hormone polyA signal (U.S. Pat. No. 5,122,458), may be present behind the transgene(s).

In certain embodiments, the recombinant adenovectors of the invention comprise as the 5′ terminal nucleotides the nucleotide sequence: CTATCTAT. These embodiments are advantageous because such vectors display improved replication in production processes, resulting in batches of adenovirus with improved homogeneity, as compared to vectors having the original 5′ terminal sequences (generally CATCATCA) (see also PCT publication no. WO 2013/135615 and U.S. Pat. No. 8,932,607), incorporated in its entirety by reference herein.

In certain embodiments the compositions comprising the recombinant adenovirus may further comprise, or are administered together with, one or more adjuvants. Adjuvants are known in the art to further increase the immune response to an applied antigenic determinant, and pharmaceutical compositions comprising adenovirus and suitable adjuvants are for instance disclosed in WO 2007/110409, incorporated by reference herein. The terms “adjuvant” and “immune stimulant” are used interchangeably herein, and are defined as one or more substances that cause stimulation of the immune system. In this context, an adjuvant is used to enhance an immune response to the RSV prefusion F proteins of the invention. Examples of suitable adjuvants include aluminium salts such as aluminium hydroxide and/or aluminium phosphate; oil-emulsion compositions (or oil-in-water compositions), including squalene-water emulsions, such as MF59 (see e.g. WO 90/14837); saponin formulations, such as for example QS21 and Immunostimulating Complexes (ISCOMS) (see e.g. U.S. Pat. No. 5,057,540; WO 90/03184, WO 96/11711, WO 2004/004762, WO 2005/002620); bacterial or microbial derivatives, examples of which are monophosphoryl lipid A (MPL), 3-O-deacylated MPL (3dMPL), CpG-motif containing oligonucleotides, ADP-ribosylating bacterial toxins or mutants thereof, such as E. coli heat labile enterotoxin LT, cholera toxin CT, and the like. It is also possible to use vector-encoded adjuvant, e.g. by using heterologous nucleic acid that encodes a fusion of the oligomerization domain of C4-binding protein (C4bp) to the antigen of interest (e.g. Solabomi et al, 2008, Infect Immun 76: 3817-23). In certain embodiments the compositions of the invention comprise aluminium as an adjuvant, e.g. in the form of aluminium hydroxide, aluminium phosphate, aluminium potassium phosphate, or combinations thereof, in concentrations of 0.05-5 mg, e.g. from 0.075-1.0 mg, of aluminium content per dose.

Administration of the compositions can be performed using standard routes of administration. Non-limiting embodiments include parenteral administration, such as by injection e.g. intradermal, intramuscular, etc, or subcutaneous, transcutaneous, or mucosal administration, e.g. intranasal, oral, and the like. Intranasal administration has generally been seen as a preferred route for vaccines against RSV. The most important advantage of the live intrasal strategy is the direct stimulation of local respiratory tract immunity and the lack of associated disease enhancement. Intranasal administration is a suitable preferred route according to the present invention as well. The advantage of intramuscular administration is that it is simple and well-established. In one embodiment of the invention the composition is administered by intramuscular injection, e.g. into the deltoid muscle of the arm, or vastus lateralis muscle of the thigh. The skilled person knows the various possibilities to administer a composition, e.g. a vaccine in order to induce an immune response to the antigen(s) in the vaccine.

Recombinant adenovirus can be prepared and propagated in host cells, according to well known methods, which entail cell culture of the host cells that are infected with the adenovirus. The cell culture can be any type of cell culture, including adherent cell culture, e.g. cells attached to the surface of a culture vessel or to microcarriers, as well as suspension culture.

Most large-scale suspension cultures are operated as batch or fed-batch processes because they are the most straightforward to operate and scale up. Nowadays, continuous processes based on perfusion principles are becoming more common and are also suitable (see e.g. WO 2010/060719, and WO 2011/098592, both incorporated by reference herein, which describe suitable methods for obtaining and purifying large amounts of recombinant adenoviruses).

Producer cells are cultured to increase cell and virus numbers and/or virus titers. Culturing a cell is done to enable it to metabolize, and/or grow and/or divide and/or produce virus of interest according to the invention. This can be accomplished by methods as such well known to persons skilled in the art, and includes but is not limited to providing nutrients for the cell, for instance in the appropriate culture media. Suitable culture media are well known to the skilled person and can generally be obtained from commercial sources in large quantities, or custom-made according to standard protocols. Culturing can be done for instance in dishes, roller bottles or in bioreactors, using batch, fed-batch, continuous systems and the like. Suitable conditions for culturing cells are known (see e.g. Tissue Culture, Academic Press, Kruse and Paterson, editors (1973), and R. I. Freshney, Culture of animal cells: A manual of basic technique, fourth edition (Wiley-Liss Inc., 2000, ISBN 0-471-34889-9).

A producer cell (sometimes also referred to in the art and herein as ‘packaging cell’ or ‘complementing cell’ or ‘host cell’) that can be used can be any producer cell wherein a desired adenovirus can be propagated. For example, the propagation of recombinant adenovirus vectors is done in producer cells that complement deficiencies in the adenovirus. Such producer cells preferably have in their genome at least an adenovirus E1 sequence, and thereby are capable of complementing recombinant adenoviruses with a deletion in the E1 region. Any E1-complementing producer cell can be used, such as human retina cells immortalized by E1, e.g. 911 or PER.C6 cells (see U.S. Pat. No. 5,994,128), E1-transformed amniocytes (See EP patent 1230354), E1-transformed A549 cells (see e.g. WO 98/39411, U.S. Pat. No. 5,891,690), GH329:HeLa (Gao et al, 2000, Human Gene Therapy 11: 213-219), 293, and the like. In certain embodiments, the producer cells are for instance HEK293 cells, or PER.C6 cells, or 911 cells, or IT293SF cells, and the like.

Typically, the adenovirus will be exposed to the appropriate producer cell in a culture, permitting uptake of the virus. Usually, the optimal agitation is between about 50 and 300 rpm, typically about 100-200, e.g. about 150, typical DO is 20-60%, e.g. 40%, the optimal pH is between 6.7 and 7.7, the optimal temperature between 30 and 39° C., e.g. 34-37° C., and the optimal MOI between 5 and 1000, e.g. about 50-300. Typically, adenovirus infects producer cells spontaneously, and bringing the producer cells into contact with rAd particles is sufficient for infection of the cells. Generally, an adenovirus seed stock is added to the culture to initiate infection, and subsequently the adenovirus propagates in the producer cells. This is all routine for the person skilled in the art.

After infection of an adenovirus, the virus replicates inside the cell and is thereby amplified, a process referred to herein as propagation of adenovirus. Adenovirus infection results finally in the lysis of the cells being infected. The lytic characteristics of adenovirus therefore permits two different modes of virus production.

The first mode is harvesting virus prior to cell lysis, employing external factors to lyse the cells. The second mode is harvesting virus supernatant after (almost) complete cell lysis by the produced virus (see e.g. U.S. Pat. No. 6,485,958, describing the harvesting of adenovirus without lysis of the host cells by an external factor). It is preferred to employ external factors to actively lyse the cells for harvesting the adenovirus.

Methods that can be used for active cell lysis are known to the person skilled in the art, and have for instance been discussed in WO 98/22588, p. 28-35. Useful methods in this respect are for example, freeze-thaw, solid shear, hypertonic and/or hypotonic lysis, liquid shear, sonication, high pressure extrusion, detergent lysis, combinations of the above, and the like. In one embodiment of the invention, the cells are lysed using at least one detergent. Use of a detergent for lysis has the advantage that it is an easy method, and that it is easily scalable.

Detergents that can be used, and the way they are employed, are generally known to the person skilled in the art. Several examples are for instance discussed in WO 98/22588, p. 29-33. Detergents can include anionic, cationic, zwitterionic, and nonionic detergents. The concentration of the detergent may be varied, for instance within the range of about 0.1%-5% (w/w). In one embodiment, the detergent used is Triton X-100.

Nuclease may be employed to remove contaminating, i.e. mostly from the producer cell, nucleic acids. Exemplary nucleases suitable for use in the present invention include Benzonase®, Pulmozyme®, or any other DNase and/or RNase commonly used within the art. In preferred embodiments, the nuclease is Benzonase®, which rapidly hydrolyzes nucleic acids by hydrolyzing internal phosphodiester bonds between specific nucleotides, thereby reducing the viscosity of the cell lysate. Benzonase® can be commercially obtained from Merck KGaA (code W214950). The concentration in which the nuclease is employed is preferably within the range of 1-100 units/ml. Alternatively, or in addition to nuclease treatment, it is also possible to selectively precipitate host cell DNA away from adenovirus preparations during adenovirus purification, using selective precipitating agents such as domiphen bromide (see e.g. U.S. Pat. No. 7,326,555; Goerke et al., 2005, Biotechnology and bioengineering, Vol. 91: 12-21; WO 2011/045378; WO 2011/045381).

Methods for harvesting adenovirus from cultures of producer cells have been extensively described in WO 2005/080556.

In certain embodiments, the harvested adenovirus is further purified. Purification of the adenovirus can be performed in several steps comprising clarification, ultrafiltration, diafiltration or separation with chromatography as described in for instance WO 05/080556, incorporated by reference herein. Clarification may be done by a filtration step, removing cell debris and other impurities from the cell lysate. Ultrafiltration is used to concentrate the virus solution. Diafiltration, or buffer exchange, using ultrafilters is a way for removal and exchange of salts, sugars and the like. The person skilled in the art knows how to find the optimal conditions for each purification step. Also WO 98/22588, incorporated in its entirety by reference herein, describes methods for the production and purification of adenoviral vectors. The methods comprise growing host cells, infecting the host cells with adenovirus, harvesting and lysing the host cells, concentrating the crude lysate, exchanging the buffer of the crude lysate, treating the lysate with nuclease, and further purifying the virus using chromatography.

Preferably, purification employs at least one chromatography step, as for instance discussed in WO 98/22588, p. 61-70. Many processes have been described for the further purification of adenoviruses, wherein chromatography steps are included in the process. The person skilled in the art will be aware of these processes, and can vary the exact way of employing chromatographic steps to optimize the process. It is for instance possible to purify adenoviruses by anion exchange chromatography steps, see for instance WO 2005/080556 and Konz et al, 2005, Hum Gene Ther 16: 1346-1353. Many other adenovirus purification methods have been described and are within the reach of the skilled person. Further methods for producing and purifying adenoviruses are disclosed in for example (WO 00/32754; WO 04/020971; U.S. Pat. Nos. 5,837,520; 6,261,823; WO 2006/108707; Konz et al, 2008, Methods Mol Biol 434: 13-23; Altaras et al, 2005, Adv Biochem Eng Biotechnol 99: 193-260), all incorporated by reference herein.

For administering to humans, the invention may employ pharmaceutical compositions comprising the recombinant adenovirus and a pharmaceutically acceptable carrier or excipient. In the present context, the term “pharmaceutically acceptable” means that the carrier or excipient, at the dosages and concentrations employed, will not cause any unwanted or harmful effects in the subjects to which they are administered. Such pharmaceutically acceptable carriers and excipients are well known in the art (see Remington's Pharmaceutical Sciences, 18th edition, A. R. Gennaro, Ed., Mack Publishing Company [1990]; Pharmaceutical Formulation Development of Peptides and Proteins, S. Frokjaer and L. Hovgaard, Eds., Taylor & Francis [2000]; and Handbook of Pharmaceutical Excipients, 3rd edition, A. Kibbe, Ed., Pharmaceutical Press [2000]). The purified recombinant adenovirus preferably is formulated and administered as a sterile solution although it is also possible to utilize lyophilized preparations. Sterile solutions are prepared by sterile filtration or by other methods known per se in the art. The solutions are then lyophilized or filled into pharmaceutical dosage containers. The pH of the solution generally is in the range of pH 3.0 to 9.5, e.g pH 5.0 to 7.5. The recombinant adenovector typically is in a solution having a suitable pharmaceutically acceptable buffer. The solution may further also contain a salt. Optionally stabilizing agent may be present, such as albumin. In certain embodiments, detergent is added. In certain embodiments, the recombinant adenovirus may be formulated into an injectable preparation. These formulations contain effective amounts of adenovirus, are either sterile liquid solutions, liquid suspensions or lyophilized versions and optionally contain stabilizers or excipients. An adenovirus vaccine can also be aerosolized for intranasal administration (see e.g. WO 2009/117134).

For instance, adenovirus may be stored in the buffer that is also used for the Adenovirus World Standard (Hoganson et al, Development of a stable adenoviral vector formulation, Bioprocessing March 2002, p. 43-48): 20 mM Tris pH 8, 25 mM NaCl, 2.5% glycerol. Another useful formulation buffer suitable for administration to humans is 20 mM Tris, 2 mM MgCl₂, 25 mM NaCl, sucrose 10% w/v, polysorbate-80 0.02% w/v. Obviously, many other buffers can be used, and several examples of suitable formulations for the storage and for pharmaceutical administration of purified (adeno)virus preparations can for instance be found in European patent no. 0853660, U.S. Pat. No. 6,225,289 and in international patent applications WO 99/41416, WO 99/12568, WO 00/29024, WO 01/66137, WO 03/049763, WO 03/078592, WO 03/061708.

In certain embodiments of the invention, use is made of an adenovirus formulation as described in WO2015/040002. Thus, in a preferred embodiment, the composition comprising the adenovirus vector comprising a nucleic acid encoding the RSV F protein of SEQ ID NO: 1 comprises in addition to the recombinant adenovirus; a citrate buffer, wherein the citrate concentration is ranging between about 5 mM and 30 mM; hydroxypropyl-beta-cyclodextrin (HBCD), wherein the concentration of

HBCD is ranging between about 1% (w/w) and 10% (w/w); a salt, e.g. sodium chloride in a concentration between about 20 mM and about 200 mM; and non-ionic detergent, e.g. Polysorbate-80 in a concentration ranging from about 0.005% (w/w) to about 0.5% (w/w); wherein said formulation has a pH ranging between 5.5 and 6.5.

In certain embodiments, the compositions have a pH ranging between about 5.7 and 6.3, and comprise citrate at a concentration ranging between about 5 and 30 mM; HBCD at a concentration ranging between 1% (w/w) and 10% (w/w); NaCl at a concentration ranging between 20 mM and 200 mM; Polysorbate-80 at a concentration ranging between about 0.01% (w/w) and 0.05% (w/w).

In certain embodiments, the compositions comprise citrate at a concentration of about 15 mM; HBCD at a concentration of about 5% (w/w); NaCl at a concentration of about 75 mM, and Polysorbate-80 at a concentration of about 0.03% (w/w).

In certain embodiments, the compositions further comprise ethanol, wherein the ethanol concentration is ranging between about 0.1% (w/w) to 1% (w/w).

In a preferred embodiment, the compositions comprise citrate at a concentration of about 15 mM; HBCD at a concentration of about 5% (w/w); NaCl at a concentration of about 75 mM, Polysorbate-80 at a concentration of about 0.03% (w/w) and ethanol at a concentration of about 0.4% (w/w). The invention is further illustrated in the following, non-limiting, examples.

EXAMPLES Example 1. Stabilizing the RSV F Protein in its Pre Fusion Conformation

Plasmids encoding basic RSV F sequences were synthesized and the amino acid substitutions were introduced in the protein by site-directed mutagenesis. The protein variants were transiently expressed in HEK293 cells. The relative protein expression on the cell surface was assessed by Flow Cytometry. The stability of the F proteins in pre-fusion conformation was evaluated in a heat-stability assay.

The protein sequence used for RSV A2 F protein variants was retrieved from the GenBank, accession number ACO83301.1. The amino acid substitutions were introduced in the sequence by site-directed mutagenesis (QuikChange II XL Site-Directed Mutagenesis Kit, Agilent technologies). The mutagenesis primers were designed using on-line tool PrimerX. HEK293T cells (CRL-11268) were purchased from American Tissue Culture Collection and cultured under standard cell culture conditions (37° C., 10% CO2).

Fully human IgG1 anti-RSV F protein antibodies CR9501 and CR9503 were constructed by cloning the heavy (VH) and light (VL) chain variable regions into a single IgG1 expression vector. PER.C6® cells (Crucell) were transfected with the IgG1 expression constructs and the expressed antibodies were purified from culture supernatants using POROS Mabcapture A chromatography (Applied Biosystems) and then buffer exchanged to 50 mM NaAc, 50 mM NaCl, pH 5.5. Antibody concentration was measured by optical absorption at 280 nm. Antibody quality was also confirmed by size-exclusion chromatography (SEC), SDS-PAGE and isoelectric focusing. The antibody CR9501 comprises VH and VL regions of 58C5 (as described in WO2011/020079) which binds specifically to RSV F protein in its pre-fusion conformation and not to the post-fusion conformation. CR9503 comprises VH and VL regions of motavizumab, which recognizes both the pre-fusion and post-fusion conformation of RSV F.

Protein Expression and Temperature Treatment

The plasmids were transiently transfected into adherent HEK293T cells using 293fectine (Cat #12347-019) transfection reagents (Life Technologies) according to suppliers recommendations. 48 hours post transfection the cells were harvested by detaching with EDTA-containing FACS buffer (no trypsin, see next section) and cell suspension was heat-treated for 10 minutes either in a water bath or in PCR block for the temperature stability experiments. After the heat-treatment, the cells were prepared for the Flow Cytometry analysis.

For analysis of adeno expressed F proteins, A549 cells were infected with Ad26 virus at a MOI of 10 000 or 5000 and Ad35 viruses at a MOI of 5000, 2500 or 1.250. After 48 h, the cells were detached and heat treated for 15 minutes at 37° C., 50° C. and 56° C. Upon heat treatment cells were stained using CR9501-Alexa647 or CR9503-Alexa647 and Propidium Iodide (PI). After staining, the cells were fixed and analyzed using the BD FACS CANTO II cell analyzer.

Flow Cytometry Analysis

For each staining, the following controls were included: 1) negative control sample. i.e. cells that were not subjected to any treatment and not stained with any antibody labeled with a fluorophore; 2) positive control samples, i.e. cells that are stained with only one fluorophore (one of each that are used for the experiment).

The cells were resuspended in the Flow Cytometry (FC Buffer, 5 mM EDTA, 1% FBS in PBS) and distributed in volumes of 50 μl of the cell suspension per well in a 96-well plate with a lid (U- or V-bottom plates). Two-step or one-step protocols were used for staining.

In case of the two-step protocol 50 μl of the first Abs (or buffer for negative controls) was added to the wells and incubated at RT for 30 min. Biotinylated CR9501 and CR9503 were used at 2 μg/ml (final concentration in a well 1 μg/ml). After incubation, the cells were washed 2 times with the FC buffer. Afterwards 50 μl of Streptavidin-APC (Molecular Probes cat #SA1005, 0.1 mg/ml is used at 1:100) or buffer for negative controls was added to the wells and incubated at RT for 30min. The cells were washed again 2 times with the FC buffer. After the last wash, the cells were resuspended in 100 μl of FC buffer+/−live-dead stain (PI from Invitrogen, cat #P1304MP, used at 2 μg/ml) and incubated at RT for 15 minutes. The cells were centrifuged at 200 g (1000 rpm) for 5 min., the buffer with PI was removed and the cells were resuspended in 150 μl of the FC buffer.

In case of a one-step protocol, CR9501 and CR9503 antibodies were labeled with fluorescent probe Alexa647 (Molecular Probes, cat #A-20186) according to manufacturer's instructions. Cells were stained according to the protocol above excluding the Streptavidin-APC step.

From the live cell population, the percentage of cells positive for CR9501/CR9503 antibody binding was determined. The cells positive for CR9503 binding express RSV F protein on their surface. The cells positive for CR9501 binding express pre-fusion RSV F on their surface.

The intensity of the antibody staining (Median fluorescence intensity—MFI) is proportional to the amount of F protein on the cell surface. MFI was calculated from the live cell population expressing F protein.

Results Surface Cell Expression of the Full Length F Protein Variants

A subset of mutations that was previously identified to increase expression or stability of the RSV F protein ectodomain in pre-fusion conformation was introduced in the wild type full length RSV A2 F sequence (accession number Genbank ACO83301). The mutations were introduced alone or in multiple combinations, and the effect on protein expression and stability was assessed.

The expression level of the protein was measured as mean fluorescence intensity (MFI) by Flow Cytometry after staining with the CR9503 antibody that is recognizing both pre-fusion and post-fusion F protein. The combination of the two amino acid substitutions that were previously described for stabilization of the soluble RSV pre-F protein (i.e. N67I and S215P) also increased the expression level of the full length RSV F protein by 2.3-fold, relative to wilde type full length RSV F (FIG. 2).

A prominent increase in expression was observed for variants with 3 amino acid substitutions combined. Interestingly, combination of more than three mutations in one variant did not further increase protein expression. This may be due to limited capacity of the cellular membrane to accommodate multiple copies of F protein.

The amount of the pre-fusion F on the surface of the cell was assessed by staining with pre-fusion specific antibody CR9501 (FIG. 3). Transfection of the cells with all F variants resulted in a more or less similar amount of pre-fusion F protein on the cell surface. Presence of the transmembrane domain stabilizes the full length protein to certain extent and therefore differences in the pre-fusion stability are not as apparent under ambient conditions between the full length F proteins. Therefore the heat-stability assay was developed to better discriminate stability of full length variants, as described below.

The A2 strain that was used as a parental sequence for the previously described F protein variants (WO2014/174018 and WO2014/202570) is a cell line adapted laboratory strain which has accumulated two unique and rare mutations (i.e. of Lysine 66 and Isoleucine 76). In the present invention, these two residues were mutated to match the natural clinical isolates (K66E, I76V). The K66E and I76V mutations were included in selected protein designs. In comparison to variants with Lys66 and Ile76, variants with glutamate at 66 (K66E) have a tendency to express slightly higher. Addition of valine at residue 76 (a double substitution of K66E and I76V) does not influence expression level when compared to variants with K66E substitution alone (FIG. 4).

Stability of the Full Length F Protein Variants on the Cell Surface

In ambient conditions on a short time scale, no significant difference in stability of pre-fusion conformation was observed between full length F variants with the different combinations of stabilizing mutations. An elevated temperature is known to serve as an efficient in vitro trigger for refolding of RSV F protein from pre-fusion to post-fusion conformation. Therefore, a heat-shock assay was established and used to assess stability of the membrane-bound full length proteins. Shortly, the HEK293T cells were transfected with the F protein constructs and used for the assay 48 hours after transfection. The cells were detached from cell culture dishes and the cell suspension was heat-treated at increasing temperatures for 10 minutes. After the heat-treatment, cells were stained with the anti-RSV F antibodies and analyzed by Flow Cytometry. The Flow Cytometry data was analyzed in two different ways. The percentage of the cells, positive for staining with the anti-F antibodies was analyzed, and also mean fluorescence intensity (MFI) of the positive cells was calculated (FIG. 5).

Both staining with CR9501 (antibody recognizing only pre-fusion F protein) and CR9503 (antibody recognizing both pre- and post-fusion F protein) were used in the Flow Cytometry assays. CR9503 antibody served as a positive control. In case when F protein loses pre-fusion conformation but still is on the surface of the cell, the protein is still detected with the CR9503 antibody. Loss of staining with both antibodies indicates that protein is not available on the cell surface for antibody binding, e.g. due to aggregation.

Full length proteins with three of more amino acid substitutions were tested in the assay and compared to the wild type RSV F. The expression of these variants was the highest and therefore these variants were preferred candidates. All of the proteins contained the N67I and S215P substitutions, and one or two extra stabilizing mutations were added.

The unmodified wild type protein had a rather stable staining with CR9503 antibody. The MFI of the CR9503 staining was elevated at higher temperatures however the spread of values was also very high. This indicated that no protein aggregation occurred after the heat-shock. Half of the pre-fusion conformation was lost after incubation of cells at approximately 55° C., after incubation of at 60° C. all pre-fusion conformation was lost as was demonstrated by decreased CR9501 binding to the wild type F samples after heat-shock at increasing temperatures.

All tested pre-fusion F protein variants were more stable than the wild type RSV F with majority of the CR9501 staining retaining also after treatment at higher temperatures (FIGS. 5 and 6). Proteins with K498R amino acid substitution were less stable than the others. Addition of the K66E mutation further stabilized the proteins as also variants with K498R amino acid substitution became as stable as others and no loss of the pre-fusion conformation was observed at 60° C. Only selected combinations of the stabilizing mutations were tested with K66E and I76V combined. All four tested proteins were stable when percentage of positive cells was analyzed, however when MFI was analyzed variant with K498R showed clear decrease in CR9501 binding after treatment with 60° C., indicating that this variant is less stable when evaluated in the temperature stress assay.

In conclusion, a combination of three stabilizing mutations (including N67I and S215P) was considered sufficient for high expression level and stability. The D486N mutations was selected as a third stabilizing mutation because of its position in the protein structure. K66E and I76V were included in the as they did not have negative effect on the protein expression and stability but made the sequence closer to naturally occurring ones.

The pre-fusion RSV F protein with the mutations K66E, N67I, I76V, S215P and D486N (F2.2) (SEQ ID NO: 1) was selected for the construction of adenoviral vectors. This protein was shown to be stable in the pre-fusion conformation in the temperature stability assay up to 60° C., and could be expressed in high levels.

Example 2. Preparation of Adenoviral Vectors Cloning RSV F Gene Into E1 Region of Ad35 and Ad26

The nucleic acid sequences, coding for the pre-fusion F proteins of the invention were gene optimized for human expression and synthesized, by Geneart. A Kozak sequence (5′ GCCACC 3′) was included directly in front of the ATG start codon, and two stop codons (5′ TGA TAA 3′) were added at the end of the RSV.pre-F coding sequence. The RSV.pre-F genes were inserted in the pAdApt35BSU plasmid and in the pAdApt26 plasmid via HindIII and Xbal sites.

Cell Culture

PER.C6 cells (Fallaux et al., 1998, Hum Gene Ther 9: 1909-1917) were maintained in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum (FBS), supplemented with 10 mM MgCl₂.

Adenovirus Generation, Infections and Passaging

All adenoviruses were generated in PER.C6® cells by single homologous recombination and produced as previously described (for rAd35: Havenga et al., 2006, J. Gen. Virol. 87: 2135-2143; for rAd26: Abbink et al., 2007, J. Virol. 81: 4654-4663). Briefly, PER.C6 cells were transfected with Ad vector plasmids, using Lipofectamine according to the instructions provided by the manufacturer (Life Technologies). For rescue of e.g. Ad35 vectors carrying the RSV.pre-F transgenes expression cassette, the pAdApt35BSU.RSV.pre-F plasmid and pWE/Ad35.pIX-rITR.dE3.5orf6 cosmid were used, whereas for Ad26 vectors carrying the RSV.pre-F transgene expression cassette, the pAdApt26.RSV.pre-F plasmid and pWE.Ad26.dE3.5orf6.cosmid were used. Cells were harvested one day after full CPE, freeze-thawed, centrifuged for 5 min at 3,000 rpm, and stored at −20° C. Next the viruses were plaque purified and amplified in PER.C6 cultured on a single well of a multiwell 24 tissue culture plate. Further amplification was carried out in PER.C6 cultured using a T25 tissue culture flask and a T175 tissue culture flask. Of the T175 crude lysate, 3 to 5 ml was used to inoculate 20×T175 triple-layer tissue culture flasks containing 70% confluent layers of PER.C6 cells. The virus was purified using a two-step CsCl purification method. Finally, the virus was stored in aliquots at −85° C.

Example 3. Induction of Immunity Against RSV F Using Recombinant Adenovirus Serotypes 26 and 35 Expressing Pre Fusion RSV F In Vivo

The immunogenicity of Ad26.RSV.preF2.1 and Ad26.RSV.preF.2.2 was evaluated in mice, comparing cellular and humoral immune responses to responses induced by identical doses of Ad26.RSV.FA2 (i.e. expressing the wild type RSV F protein). Balb/c mice (n=4 per group) were immunized with the indicated dose of 10⁸ to 10¹⁰ viral particles (vp) Ad26.RSV.FA2 or Ad26.RSV.preF2.1 or Ad26.RSV.preF2.2, or with formulation buffer. At 8 weeks after prime, the number of RSV F A2 specific IFNγ spot forming units (SFU) per 10⁶ splenocytes was determined using ELISpot. It was shown that Ad26.RSV.preF2.1 and Ad26.RSV.preF.2.2 induced increased humoral immune responses in mice when compared to Ad26.RSV.FA2, with broad neutralizing capacity and maintained cellular responses. A single intramuscular immunization with Ad26.RSV.preF2.1 and Ad26.RSV.preF.2.2 elicited a cellular response (FIG. 7) which was characterized by induction of CD8+ T cells positive for IFNγ, IL2 and/or TNFα (data not shown).

The quantity and quality of the cellular responses were comparable between Ad26.RSV.preF2.1, Ad26.RSV.preF.2.2 and Ad26.RSV.FA2. In contrast, Ad26.RSV.preF2.1 and Ad26.RSV.preF.2.2 induced significantly higher RSV neutralizing antibody titers than Ad26.RSV.FA2. Closer analysis of the antibody responses demonstrated that Ad26.RSV.preF2.1 and Ad26.RSV.preF.2.2 induced higher levels of antibodies against pre-fusion F, while post-fusion F titers remained comparable to Ad26.RSV.FA2, resulting in significantly increased preF/postF antibody ratios. In addition, the IgG2a/IgG1 ratio of the antibody response remained unaltered, demonstrating a similar Th1 skewing of the humoral response as previously demonstrated for Ad26.RSV.FA2 (FIG. 8).

For Ad26.RSV.preF2.2 it was furthermore demonstrated that the antibodies elicited were capable of neutralizing various RSV A and B strains, laboratory strains as well as clinical isolates, similar as observed for Ad26.RSV.FA2 (FIG. 9).

Subsequently, the efficacy and immunogenicity of Ad26.RSV.preF2.2 and Ad35.RSV.preF2.2 vector constructs was evaluated in the cotton rat model. These animals are permissive to replication of human RSV, with peak RSV titers in the lungs at days 4 and 5. Control groups in the experiments included groups intranasally infected with a low dose RSV A2, thereby mimicking natural exposure, as well as groups immunized with FI-RSV, using the original lot 100 that induced enhanced respiratory disease (ERD) in clinical studies in the dilution that was shown to induce ERD in cotton rats.

Single intramuscular immunization of animals with Ad26.RSV.preF2.2 in doses ranging from 10⁵ to 10⁸ vp/animal, or Ad35.RSV.preF2.2 in doses ranging from 10⁶ to 10⁹ vp/animal resulted in complete protection of the lungs from infection with the vaccine homologous RSV A2 strain, except for 3 animals immunized with 10⁵ vp Ad26.RSV.preF2.2 (FIG. 10A and 10B). Dose dependent protection of RSV replication in the nose was observed for both vectors. This ranged from full protection at 10⁸ vp/animal, to partial protection at 10⁵ vp for Ad26.RSV.preF2.2, whereas for Ad35.RSV.preF2.2, noses of animals immunized with 10⁹ vp were fully protected from RSV A2, and 10⁶ vp resulted in partial protection (FIG. 10C and 10D) Noses of animals immunized with Ad26.RSV.preF2.2 and Ad35.RSV.preF2.2 were better protected from RSV A2 infection than when immunized with their respective wild type F counterparts Ad26.RSV.FA2 and Ad35.RSV.FA2, when analyzed across dose (p=0.0003, and p=0,0001). Protection from RSV infection was accompanied by dose-dependent induction of virus neutralization titers against RSV A Long, already elicited by the lowest doses of Ad26.RSV.preF2.2 or Ad35.RSV.preF2.2 applied (FIGS. 10E and 10F). Across dose statistical comparisons of VNA A Long titers revealed that Ad26.RSV.preF2.2 is more immunogenic than Ad26.RSV.FA2 (p=0.0414), whereas elicitation of VNA titers was not significantly different between Ad35.RSV.preF2.2 and Ad35.RSV.FA2.

It was further demonstrated that Ad26.RSV.preF and Ad35.RSV.preF do not induce histopathological signs of Enhanced Respiratory Disease (ERD) after RSV A2 challenge, at any of the concentrations tested. The cotton rat is the most used and best studied model to monitor ERD. In this animal model, vaccination with FI-RSV consistently induces ERD after RSV challenge, which is visible by histopathological analysis of sections of the infected lungs for parameters as alveolitits, consisting primarily of neutrophil infiltrates, and peribronchiolitis, consisting primarily of lymphocyte infiltrates. In cotton rats, FI-RSV-induced scores for these parameters can be observed from day 1 after RSV infection, and peak at 4 to 5 days after RSV challenge.

ERD was analyzed 5 days after challenge with RSV A2 by scoring 4 parameters of pulmonary inflammatory changes (peribronchiolitis, perivasculitis, interstitial pneumonia, alveolitis). Immunization with FI-RSV resulted in enhanced scores for most histopathological markers, which was especially apparent for alveolitis (FIG. 11), the marker that was previously shown to be the most discriminating marker for ERD. No increases in alveolitis or any other ERD histopathological marker was observed in animals immunized by either Ad26.RSV.preF2.2 or Ad35.RSV.preF2.2 in a prime-only regimen after RSV challenge, even at low vaccine doses that may induce low affinity and/or low levels of antibodies (FIG. 11). This is confirming our previous results with Ad26.RSV.FA2 and Ad35.RSV.FA2 vectors.

According to the invention, it has thus been shown that Ad26.RSV.preF2.2 and Ad35.RSV.preF2.2 are potent adenoviral vectors expressing RSV F A2 which is stabilized in the pre-fusion conformation. These vectors induce strong humoral and cellular immune responses. The immune response elicited is protective against RSV A2 challenge and provides a wide range of virus neutralization in vitro against clinical and laboratory isolates of RSV. No ERD induction was observed in cotton rats after RSV exposure of vaccinated animals and therefore confirms the data generated with Ad26 and Ad35 encoding for the wild type RSV F A2 antigen. Neither mice nor cotton rats showed overt signs of reactogenicity after injection of either Ad26.RSV.preF2.2 or Ad35.RSV.preF2.2.

Example 4. Study of RSV Vaccine Recombinant Adenovirus Serotypes 26 Expressing Pre Fusion RSV F in Humans

A Randomized, Double-blind, First-in-Human Phase 1 Study to evaluate the safety, tolerability and immunogenicity of two Vaccinations of Ad26.RSV.preF, one year apart, in adults aged 60 years and older in stable health was performed. This trial has been registered at clinicaltrials.gov identifier NCT02926430.

Objectives

The primary objective of the study included assessing the safety and tolerability of 2 single doses of either 5×10¹⁰ viral particles [vp] or 1×10¹¹ vp of Ad26.RSV.preF, administered intramuscularly to adults above 60 years of age. The secondary objective included assessing the humoral and cellular immune responses as measured by virus neutralization assay (VNA), F-protein binding antibodies (pre-F and post-F ELISA) and intracellular cytokine staining (ICS).

Study Design

This is a single-center, randomized, placebo-controlled, double-blind, Phase 1 study to evaluate the safety, tolerability and immunogenicity of 2 Ad26.RSV.preF vaccinations, administered 1 year apart, in 72 male and female subjects aged 60 years and older in stable health. Subjects were randomized in parallel in a 1:1:1:1:2 ratio to 1 of 5 groups to receive 2 single intramuscular (IM) injections of study vaccine 12 months apart (Table 1).

Safety Results

An interim analysis at 28 days after first vaccination was performed. Subjects that received 5×10¹⁰ vp Ad26.RSV.preF on Day 1, were pooled together (Group 1 and 2), the same for subjects that received 1×10¹¹ vp Ad26.RSV.preF (Group 3 and 4). The primary interim analysis post first dose of all 72 subjects demonstrates that this vaccine is well tolerated at both dose levels. The median duration of solicited adverse events (AEs) typically ranged from 1 to 3.5 days. There was no serious AE related (SAE) to the vaccine, and no AEs led to withdrawal from the study. There was no apparent difference in reactogenicity between the two vaccine doses used. The interim data did not reveal an effect of dose on the safety.

In conclusion, overall solicited and unsolicited AEs reported post-vaccination were mild in the majority of subjects, transient in nature, and resolved without sequelae. Based on the above, it was concluded that both doses of Ad26.RSV.preF were safe and well-tolerated by participants of both dosage groups.

Immunogenicity Assays Pre-F ELISA

Total IgG levels against the pre-F stabilized conformation (based on RSV A2 F, Genbank ACO83301.1) were evaluated. The pre-F protein was biotinylated and sequentially captured by streptavidin coated plates on 96-well microtiter plates. Serially diluted test samples were incubated and pre-F-specific antibodies were detected with anti-human IgG antibodies conjugated with horseradish peroxidase followed by a chemiluminescent reaction. The IC₅₀ was reported as the binding titer.

Post-F ELISA

Total IgG levels against the post-F protein (RSV A2 F, Genbank ACO83301.1) were evaluated. The post-F protein was coated on 96-well microtiter plates. Serially diluted test samples were incubated and post-F-specific antibodies were detected with anti-human IgG antibodies conjugated with horseradish peroxidase followed by a chemiluminescent reaction. The IC₅₀ was reported as the binding titer.

RSV Neutralization Assay A2 Strain (A2-FFL) or B Strain (A2-BAGdup-O36634.1F-FFL)

The functionality of the vaccine-induced antibody responses was investigated by the determination of virus neutralizing antibodies (VNA) in a virus neutralization assay using A549 cells and RSV A2 virus which expresses luciferase (Luc) (RSV A2 FFL or RSV B FFL). Neutralizing antibodies were measured in A549 cells as a function of reduction in firefly Luc reporter gene expression after a single round of infection with RSV A2-FFL (or B Gdup-FFL). A fixed amount of RSV A2 FFL (or B Gdup-FFL) was mixed with a serially diluted clinical serum sample. After 1 hour incubation, A549 cells were added to the mixture. RSV A2-FFL (or B Gdup FFL) infection or inhibition was measured at 20-21 hours by the Luc reporter gene expression system. IC₅₀ was reported as the neutralization titer.

ELISpot

Frozen PBMCs were analyzed by IFNγ ELISpot. PBMCs were stimulated with peptide pools matched to the preF protein vaccine insert (SEQ ID NO: 1). The number of SFC/10⁶ stimulated PBMCs, after subtraction of mock stimulated PBMCs was reported.

CD4+ and CD8+ T-Cell Responses (ICS)

The induction or boosting of CD4 and CD8 T-cell subsets expressing IFNγ, IL-2 and TNFα was determined by ICS after RSV F-protein peptide stimulation. Total cytokine responses were reported as the percentage of CD4+ and CD8+ T cells that produce at least IFNγ, IL-2 and/or TNFα. For the Th1/Th2 balance, the CD4 cells expressing either IFNγ (Th1) or IL-4 (Th2) was reported . The total responding (log₁₀ scale) CD4+ or CD8+ T cells, expressing IFNγ, IL-2, TNFα as a single cytokine or in any combination thereof are added and reported

Immunogenicity Results

The humoral immunogenicity analysis included the following primary immuno assays (secondary objective): VNA to the RSV A2 strain and binding ELISA to pre-fusion and post-fusion F protein. In addition, a VNA to an RSV B strain was performed. Cellular immunogenicity analysis included IFNγ ELISPOT assay. The results are shown in Tables 2 -7.

As expected, RSV F specific humoral and cellular responses were detected in all subjects at baseline (day 1), reflecting a history of natural exposure to RSV throughout life (Tables 2-5).

Table 2 includes the results of VNA responses against RSV A2 strain, presented in descriptive statistics of the actual values and fold increase from baseline with corresponding 95% Confidence interval (CI) The geometric mean titer (GMT) fold rise for RSV A2 neutralizing antibodies after 1 dose of Ad26.RSV.preF at 5×10¹⁰ or 1×10¹¹ vp was 2.5 and 3.2, respectively.

The results of VNA responses against RSV B strain are shown in Table 3, which also includes descriptive statistics of the actual values and fold increase from baseline with corresponding 95% CI.

The GMT fold rise for RSV B neutralizing antibodies after 1 dose of Ad26.RSV.preF at 5×10¹⁰ or 1×10¹¹ vp was 3.1 and 3.4, respectively. Thus, both RSV A2 and RSV B neutralizing antibodies increased after vaccination at day 28 post vaccination. Ad26.RSV preF at a dose of 1×10¹¹ vp resulted in higher neutralizing antibody levels compared to the dose of 5×10¹⁰ vp.

Pre-F binding ELISA assessed the binding of antibodies to the pre-fusion conformation of the RSV F protein, while post-F binding ELISA assessed the binding of antibodies to the post-fusion conformation of the RSV F protein. Descriptive statistics of the actual values and fold increase from baseline with corresponding 95% CI of the results are presented in Table 2 for both pre-F protein binding antibody responses (ELISA) and post-F protein binding antibody responses (ELISA). Total preF IgG binding antibody showed GMT fold rises of 2.2 (5×10¹⁰ vp) and 2.9 (1×10¹¹ vp), while total postF IgG binding antibody showed GMT fold increases of 1.9 (5×10¹⁰ vp) or 2.1 (1×10¹¹ vp) fold. Thus, both the level of binding antibodies to F protein in the pre-fusion conformation (preF antibodies) and of post F antibodies increased after one vaccine dose. The results of the preF binding ELISA followed the same pattern as the VNA assay. The highest levels of preF binding antibodies was observed in the group receiving Ad26.RSV.preF at a dose of 1×10¹¹ vp. No dose response was observed on the induction of postF antibodies using 5×10¹⁰ vp or 1×10¹¹ vp Ad26.RSV.preF dose.

T-cell responses induced by Ad26.RSV.preF are measured by IFNγ ELISpot, in which PBMC are restimulated with the preF protein peptides. Descriptive statistics of the actual values of RSV-F specific T cell response (IFNγ) before and after vaccination are presented in Table 4. Median cellular responses in these elderly subjects as measured by IFNγ ELISPOT increased from 103 and 95 at baseline to 325 and 305 SFU/10⁶ PBMC (5×10¹⁰ and 1×10¹¹ vp, respectively). The total responding CD4+ T cells, expressing IFNγ, IL-2, TNFα as a single cytokine or in any combination thereof are added and presented in Table 5. An increase in the CD4+ T-cell response was observed at 28 days after after vaccination with A26.RSV.preF: the median total cytokine response was 0.03% and 0.03% at day 1 compared to 0.13% and 0.12% at day 28 post immunization (5×10¹⁰ and 1×10¹¹ vp, respectively). The total responding CD8+ T cells, expressing IFNγ, IL-2, TNFα as a single cytokine or in any combination thereof are also presented in Table 5 , the median total cytokine response was 0.07% and 0.04% at day 1 compared to 0.15% and 0.06% at day 28 post immunization (5×10¹⁰ and 1×10¹¹ vp, respectively).

As shown in Table 6, administration of Ad26.preF changed the ratio between antibodies binding to pre-fusion F (preF antibodies) and antibodies binding to post-fusion F (postF antibodies). A geometric mean increase in preF/postF ratio in the Ad26.preF vaccinated subjects was seen from 1.5 and 1.2 at baseline to 1.7 to 1.8 (5×10¹⁰ and 1×10¹¹ vp, respectively).The administration of Ad26.RSV.preF thus clearly favoured a higher rise of preF binding antibodies.

The geometric mean preF/VNA ratio in the Ad26.preF vaccinated subjects was similar for both groups (5×10¹⁰ and 1×10¹¹ vp): 0.8 at baseline and 0.7 at 28 days after vaccination (Table 7), while geometric mean postF/VNA ratio in the Ad26.preF vaccinated subjects was 0.5 and 0.6 at baseline and 0.4 and 0.4 (5×10¹⁰ and 1×10¹¹ vp, respectively) at day 29 (Table 8).

In previously conducted clinical trials VAC18192RSV1001 (ClinicalTrials.gov Identifier: NCT02440035) and VAC18192RSV1003 (ClinicalTrials.gov Identifier: NCT02561871) with the prototype Ad26.RSV FA2 RSV expressing the wild type RSV F from RSV A2, healthy subjects of 18-50 years of age received Ad26.RSV.FA2 at 5×10¹⁰ vp dose. Both humoral and cellular immune responses were increased 28 days after receiving Ad26.RSV.FA2. The geometric mean fold rise for RSV neutralizing antibodies was 2.0 and 1.9 for RSV A2 and RSV B respectively. The mean fold rise of total postF IgG binding antibody showed geometric mean increases of 3.0 fold, while the geometric mean fold rise of preF IgG binding showed a 2.4 fold rise. Median cellular responses in these subjects as measured by IFNγ ELISPOT increased from 76 to 290 SFU/10⁶ PBMC (data not shown). In these clinical trials with Ad26.RSV.FA2 an increase in preF/postF ratio was not observed. More strikingly, the geometric mean preF/post F ratio was 1.4 at baseline and decreased to 1.1 at 28 days after vaccination. The geometric mean preF/VNA ratio was 0.6 at baseline and 0.7 at 28 days after vaccination; while the geometric mean postF/VNA ratio was 0.4 at baseline and increased slightly to 0.6 at 28 days after vaccination (Tables 10-12).

In conclusion, according to the present invention it was shown that both humoral and cellular immune responses were strongly increased 28 days after the first vaccine dose for both dose levels of Ad26.RSV.preF (i.e. recombinant adenovirus encoding the RSV F protein in the pre-fusion conformation, in particular the RSV F protein of SEQ ID NO: 1). The highest humoral responses were observed with 1×10¹¹ vp dose, which was still safe. The boost in humoral immune response was preferably directed against the pre-F epitopes, as illustrated by a shift in the preF/postF binding antibody ratio from baseline. One dose of Ad26.RSV.preF was safe and well tolerated in this phase 1 study and boosted favourable humoral and cellular responses in RSV experienced older adults, even at a higher dose of 1×10¹¹ vp of adenovirus.

TABLE 1 Study design Group N Day 1 Day 365^(a) 1 12 Ad26.RSV.preF Ad26.RSV.preF (5 × 10¹⁰ vp) (5 × 10¹⁰ vp) 2 12 Ad26.RSV.preF Placebo (5 × 10¹⁰ vp) 3 12 Ad26.RSV.preF Ad26.RSV.preF (1 × 10¹¹ vp) (1 × 10¹¹ vp) 4 12 Ad26.RSV.preF Placebo (1 × 10¹¹ vp) 5 24 Placebo Placebo ^(a)For operational reasons, the second vaccination may occur between 12-14 months after the first vaccination

TABLE 2 Descriptive Statistics of the Humoral immunogenicity Assays; Full Analysis Set Ad26.RSV.preF Ad26.RSV.preF (5 × 10¹⁰ vp) (1 × 10¹¹ vp) Placebo Humoral: ELISA preF Baseline 24 24 23 DAY 1 N 24 24 23 Geometric mean (95% CI) 334 (255; 438) 407 (293; 566) 269 (212; 341) Post-dose 1 23 24 23 DAY 29 N 23 24 23 Geometric mean (95% CI) 709 (519; 967) 1193 (897; 1588) 255 (203; 321) Geometric mean increase (95% CI) 2.2 (1.7; 2.8) 2.9 (2.2; 3.9) 0.9 (0.9; 1.0) Humoral: ELISA postF Baseline 24 24 23 DAY 1 N 24 24 23 Geometric mean (95% CI) 219 (172; 279) 326 (228; 466) 174 (132; 231) Post-dose 1 23 24 23 DAY 29 N 23 24 23 Geometric mean (95% CI) 407 (305; 543) 680 (509; 908) 170 (129; 224) Geometric mean increase (95% CI) 1.9 (1.5; 2.3) 2.1 (1.8; 2.4) 1.0 (0.9; 1.0) Humoral: RSV A2 strain Baseline 24 24 23 DAY 1 N 24 24 23 Geometric mean (95% CI) 432 (328; 569) 512 (345; 759) 402 (280; 578) Post-dose 1 23 24 23 DAY 29 N 23 24 23 Geometric mean (95% CI) 1031 (839; 1267) 1617 (1126; 2323) 431 (299; 622) Geometric mean increase (95% CI) 2.5 (1.9; 3.2) 3.2 (2.3; 4.2) 1.1 (1.0; 1.1) N: number of subjects with data

TABLE 3 Titers of Neutralizing Antibodies to RSV B strain: Descriptive Statistics of the Actual Values and Fold Increase from Baseline; Full Analysis Set Ad26.RSV.preF Ad26.RSV.preF (5 × 10¹⁰ vp) (1 × 10¹¹ vp) Placebo Baseline 24 24 23 DAY 1 N 24 24 23 Geometric mean (95% CI) 1787 (1252; 2551) 2710 (1678; 4376) 1632 (1065; 2502) Post-dose 1 23 24 23 DAY 29 N 23 24 23 Geometric mean (95% CI) 5383 (3770; 7686) 9302 (6273; 13795) 1556 (1073; 2257) Geometric mean increase (95% CI) 3.1 (2.1; 4.7) 3.4 (2.3; 5) 1 (0.8; 1.1) N: number of subjects with data

TABLE 4 ELISpot: Descriptive Statistics of the Actual Values; Full Analysis Set Ad26.RSV.preF Ad26.RSV.preF (5 × 10¹⁰ vp) (1 × 10¹¹ vp) Placebo Baseline 23 21 21 DAY 1 N 23 21 21 Median (Q1; Q3) 103 (42; 175)  95 (37; 245)  114 (42; 169) Post-dose 1 23 21 22 DAY 29 N 23 21 22 Median (Q1; Q3) 325 (249; 478) 305 (172; 492)  94 (61; 223) N: number of subjects with data

TABLE 5 Total Cytokine Response (ICS): Descriptive Statistics of the Actual Values; Full Analysis Set Ad26.RSV.preF Ad26.RSV.preF (5 × 10¹⁰ vp) (1 × 10¹¹ vp) Placebo CD4 Baseline 20 20 22 DAY 1 N 20 20 22 Median (Q1; Q3)  0.03 (<0.02; 0.07)  0.03 (<0.02; 0.10) 0.02 (<0.02; 0.06) Post-dose 1 19 19 20 DAY 29 N 19 19 20 Median (Q1; Q3) 0.13 (0.08; 0.16) 0.12 (0.05; 0.18) <0.02 (<0.02; 0.04)  CD8 Baseline 20 20 22 DAY 1 N 20 20 22 Median (Q1; Q3) 0.07 (0.02; 0.20)  0.04 (<0.02; 0.12) 0.09 (<0.02; 0.31) Post-dose 1 19 19 20 DAY 29 N 19 19 20 Median (Q1; Q3) 0.15 (0.08; 0.29) 0.06 (0.03; 0.20) 0.10 (0.03; 0.66)  N: number of subjects with data

TABLE 6 Ratio Antibody Response RSV Pre F-protein versus Post F-protein over Time; Full Analysis Set Ad26.RSV.preF Ad26.RSV.preF (5 × 10¹⁰ vp) (1 × 10¹¹ vp) Placebo Baseline 24 24 23 DAY 1 N 24 24 23 Geometric mean 1.5 (1.3; 1.8) 1.2 (1; 1.6)   1.5 (1.3; 1.8) (95% CI) Post-dose 1 23 24 23 DAY 29 N 23 24 23 Geometric mean 1.7 (1.5; 2.1) 1.8 (1.4; 2.3) 1.5 (1.3; 1.8) (95% CI) N: number of subjects with data

TABLE 7 Ratio Antibody Response RSV Pre F-protein versus VNA A2 over Time; Full Analysis Set Ad26.RSV.preF Ad26.RSV.preF (5 × 10¹⁰ vp) (1 × 10¹¹ vp) Placebo Baseline 24 24 23 DAY 1 N 24 24 23 Geometric mean 0.8 (0.6; 0.9) 0.8 (0.7; 1.0) 0.7 (0.5; 0.9) (95% CI) Post-dose 1 23 24 23 DAY 29 N 23 24 23 Geometric mean 0.7 (0.5; 0.9) 0.7 (0.6; 0.9) 0.6 (0.4; 0.8) (95% CI) N: number of subjects with data

TABLE 8 Ratio Antibody Response RSV Post-F-protein versus VNA A2 over Time; Full Analysis Set Ad26.RSV.preF Ad26.RSV.preF (5 × 10¹⁰ vp) (1 × 10¹¹ vp) Placebo Baseline 24 24 23 DAY 1 N 24 24 23 Geometric mean 0.5 (0.4; 0.6) 0.6 (0.5; 0.8) 0.7 (0.5; 0.9) (95% CI) Post-dose 1 23 24 23 DAY 29 N 23 24 23 Geometric mean 0.4 (0.3; 0.5) 0.4 (0.3; 0.6) 0.6 (0.4; 0.8) (95% CI) N: number of subjects with data

TABLE 9 Descriptive Statistics of all Humoral Assays; Immunogenicity Analysis Set (Study VAC18192RSV1001 + VAC18192RSV1003) Ad26.RSV.FA2, (5 × 10¹⁰ vp) Humoral: ELISA pre Baseline 35 DAY 1 N 35 Geometric mean (95% CI) 248 (203; 304) Post-Ad.RSV.FA2 dose 35 DAY 29 N 35 Geometric mean (95% CI) 596 (493; 720) Geometric mean increase (95% CI) 2.4 (2.0; 2.9) Humoral: ELISA post Baseline 35 DAY 1 N 35 Geometric mean (95% CI) 184 (151; 224) Post-Ad.RSV.FA2 dose 35 DAY 29 N 35 Geometric mean (95% CI) 556 (445; 695) Geometric mean increase (95% CI) 3.0 (2.5; 3.7) Humoral: RSV A2 strain Baseline 35 DAY 1 N 35 Geometric mean (95% CI) 433 (345; 543) Post-Ad.RSV.FA2 dose 35 DAY 29 N 35 Geometric mean (95% CI) 856 (675; 1085) Geometric mean increase (95% CI) 2.0 (1.7; 2.4) Humoral: RSV B strain Baseline 35 DAY 1 N 35 Geometric mean (95% CI) 2231 (1851; 2689) Post-Ad.RSV.FA2 dose 23 DAY 29 N 23 Geometric mean (95% CI) 3983 (3206; 4948) Geometric mean increase (95% CI) 1.9 (1.6; 2.1) N: number of subjects with data

TABLE 10 Ratio Antibody Response RSV Pre F-protein versus Post F-protein over Time; Immunogenicity Analysis Set (Study VAC18192RSV1001 + VAC18192RSV1003) Ad26.RSV.FA2, (5 × 10¹⁰ vp) Baseline 35 DAY 1 N 35 Geometric mean (95% CI) 1.4 (1.2; 1.6) Post-Ad.RSV.FA2 dose 35 DAY 29 N 35 Geometric mean (95% CI) 1.1 (0.9; 1.2) N: number of subjects with data

TABLE 11 Ratio Antibody Response RSV Pre F-protein versus VNA A2 over Time; Immunogenicity Analysis Set (Study VAC18192RSV1001 + VAC18192RSV1003) Ad26.RSV.FA2, (5 × 10¹⁰ vp) Baseline 35 DAY 1 N 35 Geometric mean (95% CI) 0.6 (0.5; 0.7) Post-Ad.RSV.FA2 dose 35 DAY 29 N 35 Geometric mean (95% CI) 0.7 (0.6; 0.9) N: number of subjects with data

TABLE 12 Ratio Antibody Response RSV Post-F-protein versus VNA A2 over Time; Immunogenicity Analysis Set (Study VAC18192RSV1001 + VAC18192RSV1003) Ad26.RSV.FA2, (5 × 10¹⁰ vp) Baseline 35 DAY 1 N 35 Geometric mean (95% CI) 0.4 (0.3; 0.5) Post-Ad.RSV.FA2 dose 35 DAY 29 N 35 Geometric mean (95% CI) 0.6 (0.5; 0.8) N: number of subjects with data

Sequence listing Amino acid sequence of the RSV pre-fusion F protein (mutations compared to RSV A2 strain are bold and underlined) SEQ ID NO: 1: RSV preF2.2 amino acid sequence: MELLILKANA ITTILTAVTF CFASGQNITE EFYQSTCSAV SKGYLSALRT GWYTSVITIE LSNIK EI KCN GTDAK V KLIK QELDKYKNAV TELQLLMQST PATNNRARRE LPRFMNYTLN NAKKTNVTLS KKRKRRFLGF LLGVGSAIAS GVAVSKVLHL EGEVNKIKSA LLSTNKAVVS LSNGVSVLTS KVLDLKNYID KQLLPIVNKQ SCSI P NIETV IEFQQKNNRL LEITREFSVN AGVTTPVSTY MLTNSELLSL INDMPITNDQ KKLMSNNVQI VRQQSYSIMS IIKEEVLAYV VQLPLYGVID TPCWKLHTSP LCTTNTKEGS NICLTRTDRG WYCDNAGSVS FFPQAETCKV QSNRVFCDTM NSLTLPSEVN LCNVDIFNPK YDCKIMTSKT DVSSSVITSL GAIVSCYGKT KCTASNKNRG IIKTFSNGCD YVSNKGVDTV SVGNTLYYVN KQEGKSLYVK GEPIINFYDP LVFPS N EFDA SISQVNEKIN QSLAFIRKSD ELLHNVNAVK STTNIMITTI IIVIIVILLS LIAVGLLLYC KARSTPVTLS KDQLSGINNI AFSN  SEQ ID NO: 2: codon optimized nucleic acid encoding the RSV F pre-F2.2 pre-fusion protein ATGGAGCTGCTGATCCTGAAGGCCAACGCCATCA CCACCATCCTGACCGCCGTGACCTTCTGCTTCG CCAGCGGCCAGAACATCACCGAGGAGTTCTACC AGAGCACCTGCAGCGCCGTGAGCAAGGGCTACC TGAGCGCCCTGAGAACCGGCTGGTACACCAGCG TGATCACCATCGAGCTGAGCAACATCAAGGAGA TCAAGTGCAACGGCACCGACGCCAAGGTGAAGC TGATCAAGCAGGAGCTGGACAAGTACAAGAACG CCGTGACCGAGCTGCAGCTGCTGATGCAGAGCA CCCCCGCCACCAACAACAGAGCCAGAAGAGAGC TGCCCAGATTCATGAACTACACCCTGAACAACG CCAAGAAGACCAACGTGACCCTGAGCAAGAAGA GAAAGAGAAGATTCCTGGGCTTCCTGCTGGGCG TGGGCAGCGCCATCGCCAGCGGCGTGGCCGTGA GCAAGGTGCTGCACCTGGAGGGCGAGGTGAACA AGATCAAGAGCGCCCTGCTGAGCACCAACAAGG CCGTGGTGAGCCTGAGCAACGGCGTGAGCGTGC TGACCAGCAAGGTGCTGGACCTGAAGAACTACA TCGACAAGCAGCTGCTGCCCATCGTGAACAAGC AGAGCTGCAGCATCCCCAACATCGAGACCGTGA TCGAGTTCCAGCAGAAGAACAACAGACTGCTGG AGATCACCAGAGAGTTCAGCGTGAACGCCGGCG TGACCACCCCCGTGAGCACCTACATGCTGACCA ACAGCGAGCTGCTGAGCCTGATCAACGACATGC CCATCACCAACGACCAGAAGAAGCTGATGAGCA ACAACGTGCAGATCGTGAGACAGCAGAGCTACA GCATCATGAGCATCATCAAGGAGGAGGTGCTGG CCTACGTGGTGCAGCTGCCCCTGTACGGCGTGA TCGACACCCCCTGCTGGAAGCTGCACACCAGCC CCCTGTGCACCACCAACACCAAGGAGGGCAGCA ACATCTGCCTGACCAGAACCGACAGAGGCTGGT ACTGCGACAACGCCGGCAGCGTGAGCTTCTTCC CCCAGGCCGAGACCTGCAAGGTGCAGAGCAACA GAGTGTTCTGCGACACCATGAACAGCCTGACCC TGCCCAGCGAGGTGAACCTGTGCAACGTGGACA TCTTCAACCCCAAGTACGACTGCAAGATCATGA CCAGCAAGACCGACGTGAGCAGCAGCGTGATCA CCAGCCTGGGCGCCATCGTGAGCTGCTACGGCA AGACCAAGTGCACCGCCAGCAACAAGAACAGAG GCATCATCAAGACCTTCAGCAACGGCTGCGACT ACGTGAGCAACAAGGGCGTGGACACCGTGAGCG TGGGCAACACCCTGTACTACGTGAACAAGCAGG AGGGCAAGAGCCTGTACGTGAAGGGCGAGCCCA TCATCAACTTCTACGACCCCCTGGTGTTCCCCA GCAACGAGTTCGACGCCAGCATCAGCCAGGTGA ACGAGAAGATCAACCAGAGCCTGGCCTTCATCA GAAAGAGCGACGAGCTGCTGCACAACGTGAACG CCGTGAAGAGCACCACCAACATCATGATCACCA CCATCATCATCGTGATCATCGTGATCCTGCTGA GCCTGATCGCCGTGGGCCTGCTGCTGTACTGCA AGGCCAGAAGCACCCCCGTGACCCTGAGCAAGG ACCAGCTGAGCGGCATCAACAACATCGCCTTCA GCAACTGA  

1. A method of inducing a safe immune response against respiratory syncytial virus (RSV) in a human subject in need thereof, comprising administering to the human subject a composition comprising a replication-deficient recombinant adenovirus comprising a nucleic acid encoding an RSV Fusion (F) protein comprising the amino acid sequence of SEQ ID NO: 1, and a pharmaceutically acceptable carrier, wherein the recombinant adenovirus is administered in a total dose of from about 1×10¹⁰ to about 2×10¹¹ viral particles (vp).
 2. The method according to claim 1, wherein the total dose is from about 5×10¹⁰ to about 1×10¹¹ viral particles (vp).
 3. The method according to claim 1, wherein the immune response comprises the induction of antibodies specifically binding to RSV F protein.
 4. The method according to claim 1, wherein the immune response comprises the induction of RSV neutralizing antibodies.
 5. The method according to claim 1, wherein the immune response comprises the induction of antibodies specific for the RSV F protein in the pre-fusion conformation and antibodies specific for the RSV F protein in the post-fusion conformation, and wherein the geometric mean titer (GMT) increase of antibodies specific for RSV F protein in the pre-fusion conformation is higher than the geometric mean titer (GMT) increase of antibodies specific for RSV F protein in the post-fusion conformation, in enzyme linked immunosorbent assays (ELISAs).
 6. The method according to claim 1, wherein the ratio between the geometric mean titer (GMT) increase of post-fusion F specific antibodies as measured in ELISA and the geometric mean titer (GMT) increase of neutralizing antibodies as measured in a VNA assay is reduced after administration of said composition as compared to said ratio before administration of said composition.
 7. The method according to claim 1, wherein the immune response further comprises a cellular response as indicated by IFNgamma producing T cells as measured in an IFNγ ELISPOT in response to stimulation with a pool of peptides covering the RSV F protein of SEQ ID NO: 1, and/or by measurement of CD4 and CD8 T-cell subsets expressing IFNγ, IL-2 and TNFα by intracellular staining (ICS) after stimulation with a pool of peptides covering the RSV F protein of SEQ ID NO:
 1. 8. The method according to claim 1, wherein the subject is a human of 60 years or older.
 9. The method according to claim 1, wherein the nucleic acid encoding the RSV F protein comprises the nucleic acid sequence of SEQ ID NO:
 2. 10. The method according to claim 1, wherein the recombinant adenovirus is a human adenovirus.
 11. The method according to claim 10, wherein the recombinant adenovirus is of serotype 26 or
 35. 12. The method according to claim 1, wherein the composition is administered intranasally.
 13. The method according to claim 1, further comprising administering to the human subject the composition one year after the initial administration of the composition.
 14. A method of inducing a safe immune response against respiratory syncytial virus (RSV) in a human subject in need thereof, comprising administering to the human subject a composition comprising a replication-deficient recombinant adenovirus serotype 26 (Ad26) comprising the polynucleotide sequence of SEQ ID NO: 2, and a pharmaceutically acceptable carrier, wherein the recombinant Ad26 is administered in a total dose of from about 1×10¹⁰ to about 2×10¹¹ viral particles (vp).
 15. The method according to claim 14, wherein the total dose is from about 5×10¹⁰ to about 1×10¹¹ viral particles (vp).
 16. The method according to claim 15, wherein the composition is administered intranasally.
 17. The method according to claim 14, wherein the composition is administered intranasally.
 18. The method according to claim 14, wherein the subject is a human of 60 years or older.
 19. The method according to claim 14, further comprising administering to the human subject the composition one year after the initial administration of the composition.
 20. The method according to claim 14, wherein the immune response comprises the induction of RSV neutralizing antibodies. 